1. Field of the Invention
The present invention relates to a reel torque device for a video cassette tape recorder, and more particularly to a reel torque device for a video cassette tape recorder wherein a single clutch mechanism is used for transmitting drive forces of different torques to a supply reel and a take-up reel.
2. Description of Related Art
Referring to FIG. 1, there is shown a generally used video cassette tape recorder. As shown in the drawing, the recorder comprises a supply reel gear 1, a take-up clutch gear 2, a middle gear 3 disposed between the supply reel gear 1 and the take-up clutch gear 2 to rotate by a capstan motor (not shown), and a supply idler gear 4 and a take-up idler gear 4' disposed at both sides of the middle gear 3 to engage always with the middle gear 3 and adapted to selectively engage the supply reel gear 1 and the take-up clutch gear 2 with the middle gear 3, depending on the rotation direction of the middle gear 3, respectively. According to this construction, the supply reel gear 1 and the take-up clutch gear 2 are selectively rotated by the rotation of the middle gear 3.
That is, as the middle gear 3 rotates in the direction of the arrow A indicated in FIG. 1, that is in a counter-clockwise direction, the supply idler gear 4 rotates by itself in the direction of the arrow C, that is in clockwise direction, about its center and simultaneously moves along the periphery of the middle gear 3 about the center of middle gear 3 in the direction of the arrow B, that is counter-clockwise. As a result, the idler gear 4 engages with the supply reel gear 1, thereby causing the supply reel gear 1 to rotate in the direction of the arrow D, that is in the counter-clockwise direction. On the other hand, as the middle gear 3 rotates in the direction of the arrow A' indicated in FIG. 1, that is in the clockwise direction, the take-up idler gear 4' rotates by itself in the direction of the arrow C', that is in the counter-clockwise, about its center and simultaneously moves along the periphery of the middle gear 3 about the center of middle gear 3 in the direction of the arrow B', that is in the clockwise direction. As a result, the idler gear 4' engages with the take-up clutch gear 2, thereby causing the take-up clutch gear 2 to rotate clockwise in the direction of the arrow D'.
Generally, the torque required for rotating the supply reel gear 1 should be higher than that required for rotating the take-up clutch gear 2.
A typical example of generally used reel torque devices of video cassette tape recorders will now be described in conjunction with FIGS. 1 and 2.
As shown in FIGS. 1 and 2, the reel torque device mainly comprises a supply reel table S, a middle gear assembly C, and a take-up reel table T. The supply reel table S includes a reel body 5 having an upright shaft portion 5a. Around the upright shaft portion 5a of the reel shaft 5, the supply reel gear 1, a frictional plate 7 provided at the lower surface thereof with a felt 6 and a reel disc 8 are fitted, in turn. The reel disc 8 has a shaft portion 8a provided with a recess 8b. In the recess 8b, a compression coil spring 9 is disposed and adapted to always urge the felt 6 of the frictional plate 7 against the upper surface of the supply reel gear 1. A reel cap 12 is closely fitted around the upper end of the shaft portion 5a of reel body 5. Around the shaft portion 8a of reel disc 8, a reel sleeve 11 and a compression coil spring 10 are disposed between the reel cap 12 and the lower portion of the reel of the reel disc 8. The compression coil spring 10 functions to urge the reel sleeve 11 against the reel cap 12.
On the other hand, the middle gear assembly C includes the middle gear 3 rotatably mounted to a shaft 14 and provided with an upper recess. To the upper end of the shaft 14, a main base plate 13 is fixedly mounted. In the recess of the middle gear 3 and beneath the main base plate 13, a spring guide 15, a compression coil spring 16, an idler arm 17 and a felt 18 are disposed, in turn, around the shaft 14. The idler arm 17 has at the middle end thereof a pair of downwardly extending shafts 19 (in FIG. 2, only one shaft is shown). To the shafts 19, the supply idler gear 4 (not shown in FIG. 2) and the take-up idler gear 4' are mounted to engage always with the middle gear 3 and adapted to selectively engage the supply reel gear 1 and the take-up clutch gear 2 with the middle gear 3, depending on the rotation direction of the middle gear 3, respectively. A belt guide groove 3a is formed at the lower portion of the middle gear 3 so that the middle gear 3 is connected with the capstan pulley 20 by means of a belt 21.
Also, the take-up reel table T has a reel body 22 having an upright shaft portion 22a. Around the shaft portion 22a of the reel body 22, the take-up clutch gear 2 is fitted. Above the take-up clutch gear 2, a take-up reel gear 25 is fitted around the shaft portion 22a of the reel body 22. A felt 24 is disposed at the lower surface of the take-up reel gear 25. Between the reel body 22 and the take-up clutch gear 2, a compression coil spring 23 is disposed and adapted to urge the take-up clutch gear 2 against the felt 24 attached to the lower surface of the take-up reel gear 25.
In the above construction of a conventional reel torque device, the drive force of the capstan motor is transmitted to the middle gear 3, via the capstan pulley 20 and the belt 21, thereby causing the middle gear 3 to rotate. According to the rotation of middle gear 3, the idler arm 17 rotates clockwise or counter-clockwise about the center shaft 14, by virtue of the frictional contact generated between the middle gear 3 and the idler arm 17 and resiliently supported by the compression coil spring 16.
Therefore, as the middle gear 3 rotates in the direction of the arrow A of FIG. 1, the supply idler gear 4 engages with the supply reel gear 1, so that the rotational force of the middle gear 3 is transmitted to the reel disc 8, via the idler arm 17, the supply idler gear 4, the supply reel gear 1, the felt 6 and the frictional plate 7. At this time, the torque for transmitting the rotational force is determined by the relative rotation torque generated between the supply reel gear 1 and the frictional plate 7 by the frictional contact between the felt 6 and the supply reel gear 1.
On the other hand, as the middle gear 3 rotates in the direction of the arrow A' of FIG. 1, the take-up idler gear 4' engages with the take-up clutch gear 2, so that the rotational force of the middle gear 3 is transmitted to the reel disc 8, via the idler arm 17, the take-up idler gear 4', the take-up clutch gear 1, the felt 24 and the take-up reel gear 25. At this time, the torque for transmitting the rotational force is determined by the relative rotation torque generated between the take-up clutch gear 2 and the take-up reel gear 25 by the frictional contact between the felt 25 and the take-up clutch gear 2.
That is, the rotation torque of the supply reel table S can be adjusted to be higher than the rotation torque of the take-up reel table T, by properly adjusting the modulus of elasticity of the compression coil spring S constituting a part of the supply reel table S and the coefficient of friction of the felt constituting a part of the take-up reel table T.
However, the construction of the conventional device is complex, since the supply reel table 8 and the take-up reel table T include torque devices, respectively, thereby causing the manufacture cost to be increased and the productivity to be reduced. As a result, it is impossible to apply the conventional device to camera-integrated video cassette tape recorders (also, referred to as camcorders) which require compact and light construction.
In the conventional device, rotation transmission systems between respective torque devices and respective parts receiving the drive force from the belt 21 have a long rotation force transmitting distance. Accordingly, a relatively large load is generated in initial driving operations, for example, in the conversion from stop mode to rewinding operation mode, thereby causing the belt 21 to slip and thereby wear. Consequently, the life of belt 21 is reduced.